A magnetic random access memory (hereafter, also referred to as a MRAM) is known, which uses a magneto-resistive element as a storage element. As the magneto-resistive element, an element is known, which indicates a magnetic resistive effect such as an AMR (Anisotropic Magneto-Resistance) effect, a GMR (Giant Magnet-Resistance) effect and a TMR (Tunnel Magneto-Resistance) effect.
A TMR structure and a magnetic random access memory using the same as a storage element are disclosed in, for example, 2000 IEEE International Solid-State Circuits Conference DIGEST OF TECHNICAL PAPERS, P.128, and 2000 IEEE International Solid-State Circuits Conference DIGEST OF TECHNICAL PAPERS, P.130. Also, U.S. Pat. No. 6,545,906 discloses a toggle write mode as one of data writing methods in a MRAM.
In those data wiring methods to the MRAM, an inversion magnetic field required to switching a magnetization of a free layer becomes greater, approximately inversely proportional to a size of a memory cell. In short, as the memory cell is made miniaturized, a write current tends to be increased.
As a writing method which can suppress an increase in a write current in association with miniaturization, a spin transfer process is disclosed in, for example, Grollier et al., “Spin-polarized current induced switching in Co/Cu/Co pillars”, Applied Physics Letters, Vol. 78, pp. 3663, 2001. This spin transfer process uses a magneto-resistive element having a structure in which two Co-magnetic material films whose thicknesses are different are laminated through a Cu layer. When a current is supplied by applying a voltage to this magneto-resistive element in a lamination direction, a resistance value between the magnetic materials can be changed on the basis of a polarity of the current. A data storing is carried out by correlating a data to the resistance value.
As a principle of the spin transfer process, when electrons are supplied from the thick magnetic material side, a magnetization direction of the thin magnetic material becomes the same magnetization direction as the thick magnetic material. That is, the magnetizations become parallel. This is because spin electrons, on which the magnetization direction of the thick magnetic material is reflected, are transferred to the thin magnetic material. On the other hand, when electrons are supplied from the thin magnetic material side, the magnetization direction of the thin magnetic material becomes opposite to the magnetization direction of the thick magnetic material. That is, the magnetizations are anti-parallel. This is because, when electrons are supplied from the thin magnetic material side, spin electrons of which magnetization direction does not coincide with that of the thick magnetic material remains in the thin magnetic material.
FIG. 1 is a schematic view showing situations of magnetization switching in a spin transfer process. A magneto-resistive element 101 includes a free layer 102 and a pinned layer 104 which are magnetic layers, and a tunnel barrier layer 103 of a non-magnetic layer which is sandwiched between the free layer 102 and the pinned layer 104. Here, the pinned layer 104 whose magnetization direction is fixed is formed to be thicker than the free layer 102. The state in which the magnetization directions of the free layer 102 and the pinned layer 104 are parallel is correlated to a data “0”, and the state in which they are anti-parallel is correlated to the data “1”.
The magnetization switching in the spin transfer process is attained by a CPP (Current Perpendicular to Plane) process, and a write current IW is supplied vertically to a material surface. Specifically, at a time of a shift to a data “0” from a data “1”, the write current IW is transferred from the free layer 102 to the pinned layer 104. In this case, electrons e-having the same spin state as that in the pinned layer 104 is inversely moved to the free layer 102 from the pinned layer 104. The spin electrons, on which the magnetization direction of the thick pinned layer 104 is reflected, is considered to be transferred to the thin free layer 102. Thus, the magnetization of the free layer 102 is switched and becomes the same magnetization direction of the pinned layer 104 (becomes “0”).
At a time of a shift to the data “1” from the data “0”, the write current IW is supplied from the pinned layer 104 to the free layer 102. In this case, electrons e-having the same spin state as that in the pinned layer 104 is inversely moved from the free layer 102 to the pinned layer 104. When electrons is supplied from the thin free layer 102, spin electrons, of which states do not coincide with the magnetization direction of the thick pinned layer 104, remains in the free layer 102. Thus, the magnetization of the free layer 102 is switched and becomes the same magnetization direction of the pinned layer 104 (becomes “1”).
In this way, in the magnetization switching of the spin transfer process, a data is written by movement of spin electrons. The magnetization direction of the free layer 102 can be defined on the basis of the direction of the write current IW transferred vertically to the material surface. Here, it is known that a threshold of writing (the magnetization switching) depends on a current density. Thus, as a size of a memory cell is miniaturized, the write current necessary for the magnetization switching is decreased. That is, since the write current IW is decreased based on miniaturizing a structure of the memory cell, the magnetization switching of the spin transfer process is important to attain a large capacity of the MRAM. However, as for the magnetization switching based on the spin transfer process as mentioned above, principles are considered to be different between cases of switching directions (“1” to “0” and “0” to “1”). Thus, write properties are different on the basis of the switching directions, and a control of the writing is complicated.
As a related technique, Japanese Laid-Open Patent Application (JP-P 2004-193346A) discloses a magnetic memory and a magnetic memory manufacturing method. This magnetic memory includes a substrate; a first insulating film, a plurality of first signal lines, a plurality of memory cells, a first inter-layer insulating film, a second insulating film formed on the first inter-layer insulating film, and a plurality of second signal lines. The first insulating film is formed on the top surface side of the substrate. The plurality of first signal lines is embedded in the first insulating film and formed to extend to a first direction. Each of the plurality of memory cells is formed on each of the plurality of first signal lines and includes a magneto-resistive element having a spontaneous magnetization in which a magnetization direction is switched on the basis of a stored data. The first inter-layer insulating film is formed to surround the plurality of memory cells, on the first insulating film and the plurality of first signal lines. The second insulating film is formed on the first inter-layer insulating film. The plurality of second signal lines is embedded in the second insulating film and formed to extend to a second direction substantially vertical to the first direction. At least one of the first insulating film and the second insulating film includes a magnetic material of high magnetic permeability. Each of the plurality of memory cells is arranged at each of positions at which the plurality of first signal lines and the plurality of second signal lines intersect.
Japanese Laid-Open Patent Application (JP-P 2005-50907A) discloses a magnetic resistive effect element and a magnetic memory. This magnetic resistive effect element includes a first magnetization pinned layer, a second magnetization pinned layer, a magnetic recording layer, a tunnel barrier layer and a middle layer. The first magnetization pinned layer has a magnetic layer of at least one layer, and a spin direction is pinned. The second magnetization pinned layer has a magnetic layer of at least one layer, and a spin direction is pinned. The magnetic recording layer has a magnetic layer of at least one layer formed between the first magnetization pinned layer and the second magnetization pinned layer, and a spin direction is variable. The tunnel barrier layer is formed between the first magnetization pinned layer and the magnetic recording layer. The middle layer is formed between the magnetic recording layer and the second magnetization pinned layer.
Japanese Laid-Open Patent Application (JP-P 2005-150482A) discloses a magnetic resistive effect element and a magnetic memory. This magnetic resistive effect element includes a magnetization free layer, and a first magnetic layer and a second magnetic layer, which are formed on both sides of this magnetization free layer and magnetically separated from each other, and magnetization directions of the magnetic layers are pinned oppositely to each other. A magnetic moment number per unit area in the first magnetic layer and the second magnetic layer may be greater than that of the magnetization free layer.
Japanese Laid-Open Patent Application (JP-P 2005-166896A) discloses a magnetic resistive effect element and a first wiring layer. The magnetic resistive effect element includes a magnetization pinned layer whose magnetization direction is pinned, a storage layer whose magnetization direction is variable, and a tunnel barrier layer formed between the magnetization pinned layer and the storage layer. The first wiring layer is electrically connected to the magnetic resistive effect element and extends to a direction orthogonal to a magnetization easy axis direction of the storage layer. The end surface of the magnetic resistive effect element orthogonal to the magnetization easy axis direction and the end surface of the first wiring layer orthogonal to the magnetization easy axis direction are located on the same flat surface.
Japanese Laid-Open Patent Application (JP-P 2005-175374A) discloses a magnetic memory device and a manufacturing method of the same. This magnetic memory device includes a first magnetic material layer, a tunnel magneto-resistive element, a first conductive wiring and a second conductive wiring. The first magnetic material layer is a magnetization pinned layer. The tunnel magneto-resistive element is formed such that a tunnel barrier layer is sandwiched between the tunnel magneto-resistive element and a second magnetic material layer as a magnetization free layer whose magnetization direction can be changed. A spin direction of the second magnetic material layer is parallel or anti-parallel to a spin direction of the first magnetic material layer. Correspondingly thereto, information is stored. The first conductive wiring is electrically insulated from the tunnel magneto-resistive element. The second conductive wiring crosses this first conductive wiring and is electrically connected to the tunnel magneto-resistive element. With regard to a pair of end sides of the second magnetic material layer and a pair of end sides of the first magnetic material layer, which exist in a direction of a magnetic moment of the second magnetic material layer, a distance between one end side of the second magnetic material layer and one end side of the first magnetic material layer located on the same side as the foregoing end side is substantially equal to a distance between the other end side of the second magnetic material layer and the other end side of the first magnetic material layer located on the same side as the foregoing end side.